The present invention is generally related to porous silicon substrates and, more particularly, is related to a method for photoluminescence enhancement, photoluminescence stabilization, and the metallization of porous silicon substrates.
High surface area porous silicon (PS) substrates formed in wafer scale through electrochemical (EC) etching fall into two groups. PS substrates fabricated from aqueous electrolytes consist of highly branched nonporous substrates while PS substrates fabricated from a nonaqueous electrolyte are comprised of open and accessible macroporous substrates with deep, wide, well-ordered channels.
High-surface area substrates formed in wafer scale through etching display a visible photoluminescence (PL) upon excitation (PLE) with a variety of visible and ultraviolet light sources. This room-temperature luminescence has attracted considerable attention primarily because of its potential use in the development of silicon-based optoelectronics, displays, and sensors.
Although the PL is thought to emanate from regions near the PS substrate surface, the origin of the PL is the source of some controversy as the efficiency and wavelength range of the emitted light can be affected by the physical and electronic properties of the surface, the nature of the etching solution, and the nature of the environment into which the etched sample is placed. Given this range of parameters, it is surprising that, with few exceptions, PL spectra are reported for PS substrates formed in dilute aqueous HF solutions, that have already been dried in air or more inert environments following etch and rinse treatments. These ex situ samples, while providing spectral information, do not indicate the evolution of the PS substrates, and thus, they do not indicate means by which it might be modified and enhanced during or following the etch treatment.
An existing problem in fabricating PS devices rests with establishing electrical contact to the PS substrates. Another problem with PS includes the relatively long excited-state lifetime associated with the PS substrate PL. A further problem includes the relatively low PL quantum yield and the instability of the PL from PS substrates.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.
An embodiment of the present invention provides for a post-etch treatment method of enhancing and stabilizing the PL from a PS substrate. The method includes treating the PS substrate with an aqueous hydrochloric acid (HCl(H2O)) solution and then treating the PS substrate with an alcohol. Another exemplary embodiment provides a post-etch method of enhancing and stabilizing the PL from a PS substrate, which includes treating the PS substrate with an HCl(H2O) and alcohol solution.
Still another embodiment provides a post-etch method for metallizing a PS substrate in an electroless environment. The method includes treating the PS substrate with an HCl(H2O) solution and then treating the PS substrate with an alcohol, or alternatively, treating the PS substrate with a hydrochloric acid/alcohol solution. Subsequently, the PS substrate is treated with a hydrazine solution to remove fluorides from the PS substrate. Next, a metal-containing electroless solution is introduced to the PS substrate. Thereafter, the PS substrate is illuminated with a light source at wavelengths less than about 750 nanometers to cause PL of the PS substrate. Then, the metal from the metal-containing solution is induced by the PL to reduce onto the PS substrate (e.g. metallization).
A further embodiment provides for a post-etch method of enhancing PL from a PS substrate by treating the PS substrate with a dye. The dye can be selected from the group including, but not limited to 3,3-diethyloxadicarbacyamine iodide; Rhodamine dye compounds; Fluorocein; and dicyanomethylene (DCM) dye compounds.
Still a further embodiment provides for a metallized PS substrate. The PS substrate can be metallized with copper, silver, or other appropriate metal and can have a resistance of about 20-100 ohm.
Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.